There have been a number of techniques historically utilized to fuse smaller joints in a living body such as finger joints and toe joints. The use of K wires arranged in a cross or parallel fashion complimented with dental wiring to augment the fixation has also been proposed. Moreover, the use of a cone and cup technique coupled with a K wire fixation technique has also been proposed. The use of small screws and plates to supplement fixation of bony surfaces as well as several novel screw systems such as marketed by Howmedica and described in U.S. Pat. No. 5,417,692 have also been proposed for fixation of bones for fusion.
With the development of arthritic conditions of the metacarpal phalangeal joints, such as commonly seen in patients with rheumatoid arthritis, as well as arthritic conditions of the proximal interphalangeal joint, such as commonly seen in patients with rheumatoid and osteoarthritis, a number of devices have been proposed to alleviate the severe pain, deformity, and disability arising out of the arthritic destruction of these joints. One proposal involves the use of a silicone implant arthroplasty as a spacer coupled with reconstruction and realignment of adjacent ligaments and tendons to effect a satisfactory joint replacement in metacarpal and proximal interphalangeal joints of the hand. Such devices have also been used in the metacarpal phalangeal joint of the foot as well as other interphalangeal joints to a lesser degree. Use of these devices, however, in distal interphalangeal joints is frequently associated with failure due to the excessive forces across these joints.
While these artificial joints act as spacers, they are fraught with a difficulty of long-term failure due to the resorption of adjacent bone and the lack of permanent fusion or fixation. Thus, these joints act merely as spacers, and do not provide a degree of intrinsic stability, nor do they physically bond or become attached to the adjacent bone. Instead, they are surrounded with a membrane representative of a giant cell reaction or foreign body reaction.
U.S. Pat. No. 5,108,443 to P. Branemark and issued Apr. 28, 1992, discloses a technique wherein a screw assembly is placed in a bone that appears to be fairly uniform in cross-section between opposite ends thereof. This technique fails to take into account the proximal widening of bones known in the metaphysis, and the substantial mismatch of size and canal diameters that can occur in both normal and especially arthritic bone. Similarly structured devices also fail to allow a variability of size mismatch wherein the proximal phalanx of a hand may be substantially asymmetrical in size with the standard sizes available that would correspond to a metacarpal phalangeal joint within the enormity of population ranges sized by these systems. This lack of variability can lead to difficulty with stability of a finger joint implant, wherein the metacarpal phalangeal joint side may be quite rigid, but the proximal phalangeal side alternatively may be loose. Attempts to place a large implant to accommodate the loose proximal interphalangeal side may be fraught with excessive resection of bone on the metacarpal phalangeal joint side in order to accommodate the large size implant to obtain stability.
Grommets have also been proposed for use to provide rotational control, but do not take into account the size mismatch that can occur. This lack of variability of implants can be found both for enlargement of either the distal or proximal bone abnormally compared to the corresponding opposable bony surface. This can especially occur in metacarpal phalangeal joints, but alternatively can occur in proximal and distal interphalangeal joints of the hands. This lack of size variability due to the lack of modularity is a substantial problem and can lead to late failure with rotary changes and provide a substantial loss of stability and function as well as a decreased cosmetic result.
Thus, there is a need and a desire for an improved joint assembly that can be used as a distal interphalangeal joint, a proximal interphalangeal joint, or as a metacarpal phalangeal joint as required. There is also a need and a desire for a joint assembly that addresses long-term fixation needs, the rigidity of fixation relative to the bones, and the ease of interchangability in the case of failure with a solidly anchored support.